1. Field of the Invention
The present invention relates to an improvement in an imaging device and an image blurring correction device, each of which employs an angular velocity sensor and a high-pass filter configured to perform a detection of an angular velocity that is caused by a movement of a shaking hand of the imaging device and correct the image blurring that may result therefrom.
2. Description of the Related Art
An imaging device that includes an image blurring correction device, which corrects a blurring of an image, is conventionally known. The image blurring correction device employs an angular velocity sensor and a high-pass filter to perform a detection of an angular velocity in accordance with a movement of a shaking hand (for reference, see Japanese Patent Application Publication No. 2004-215189). The angular velocity sensor detects a blurring that results from a vibration of a camera, and outputs a blurring signal.
The high-pass filter, which is configured from a capacitor and a resistor, is employed to eliminate an offset, i.e., a direct current component, of the blurring signal that arises from such as a drift or the like on the part of the angular velocity sensor. The blurring signal that results after being passed through the high-pass filter, i.e., an alternating current that gives rise to the blurring, is employed as an angular velocity signal. The correction of the blurring of the image is performed in accordance with the angular velocity signal that results therefrom.
On the other hand, a frequency of the blurring signal that arises from the movement of the shaking hand is typically on the order of between about 1 Hz and 20 Hz. Accordingly, a cut-off frequency of the high-pass filter must be less than 1 Hz to a degree sufficient to allow the image blurring that arises from the movement of the shaking hand to be reliably corrected. The cut-off frequency of the high-pass filter is thus set to a value on the order 0.1 Hz.
Accordingly, a time constant of the high-pass filter is on the order of τ=1/(2π×0.1)=1.6 seconds. Setting such a time constant, however, necessitates on the order of 6×τ=approximately 10 seconds in order for the angular velocity signal to be normalized when a significant fluctuation occurs with the angular velocity signal thereof.
Accordingly, when panning while taking a photograph, i.e., moving a camera body 1 from left to right, or vice versa, such as is illustrated in FIG. 1, as an instance thereof, a phenomenon occurs in accordance with a change in a direction of the camera 1, such as is described hereinafter.
In FIG. 1, reference numeral A1 denotes a rotational driving operation commencement period, which is for rapidly orienting the camera body 1, which is in a static state, toward a subject of a photograph, reference numeral A2 denotes a rotational driving photography period, wherein the camera body 1 is moved in a rotational driving manner at a given angular velocity in order to take a pan photograph, reference numeral A3 denotes a rotation operation termination period, wherein the rotational driving of the camera body 1 is halted after the taking of the pan photograph is completed, and reference numeral A4 denotes a static state period, wherein the camera body 1 is maintained in a static state, following the halting of the rotational driving of the camera body 1.
A transition curve Q of an actual angular velocity, i.e., a true angular velocity, of the camera body 1 when taking the pan photograph is denoted by a solid line in FIG. 2, and a transition curve Q of the angular velocity signal of the camera body 1 when taking the pan photograph is shown by a dashed line in FIG. 2. A horizontal axis denotes units of time, and a vertical axis denotes a scale value that corresponds to either the angular velocity or a voltage.
In the rotational driving operation commencement period A1, the actual angular velocity of the camera body 1 is increased from zero, such as is denoted by reference numeral Q1, as a result of the rapid rotational driving operation of the camera body 1. In the rotational driving photography period A2, the actual angular velocity of the camera body 1 reaches a constant value, such as is denoted by reference numeral Q2. In the rotation operation termination period A3, the actual angular velocity of the camera body 1 declines such as is denoted by reference numeral Q3, owing to the halting of the rotational driving of the camera body 1. In the static state period A4, the actual angular velocity of the camera body 1 reaches zero, such as is denoted by reference numeral Q4.
When performing a tilt photograph, by tilting the camera body 1 in order to orient the camera body 1 toward the subject of the photograph, it is to be understood that the transition of the angular velocity of the camera body 1 thereupon denotes a transition that is similar to the transition of the actual angular velocity of the camera body 1 when taking the pan photograph.
On the contrary, in the rotational driving operation commencement period A1, the camera body 1 is accelerated from the static state so as to be rotationally driven in a constant direction, the capacitor in the high-pass filter is charged, and an angular velocity signal Q′ that is outputted by the angular velocity sensor increases such as is denoted by reference numeral Q1′. In the rotational driving photography period A2, the angular velocity signal Q′ declines such as is denoted by reference numeral Q2′ in order to discharge the charge that is accumulated in the capacitor in the high-pass filter according to the time constant of the high-pass filter. In the rotation operation termination period A3, the angular velocity Q of the camera body 1 is decelerated, i.e., the camera body 1 is accelerated in an opposite direction, whereupon the charge in the capacitor in the high-pass filter is rapidly discharged, the angular velocity signal Q′ rapidly declines such as is denoted by reference numeral Q3′, and the capacitor is charged in the opposite direction. In the static state period A4, the actual angular velocity Q of the camera body 1 reaches zero such as is denoted by reference numeral Q4, whereupon the charge that is accumulated in the capacitor in the high-pass filter is discharged according to the time constant of the high-pass filter, and the angular velocity signal Q′ increases such as is denoted by reference numeral Q4′.
Put another way, whereas the transition of the actual angular velocity Q of the camera body 1 and the transition of the angular velocity signal Q′ correspond to the rotational motion operation commencement period A1 and the rotation operation termination period A3, the angular velocity signal Q′ is observed to decline because the angular velocity signal Q′ declines as a consequence of the discharge of the charge in accordance with the time constant of the high-pass filter with regard to the rotational driving photography period A2, which is intended to maintain a constant angular velocity.
In contrast, the angular velocity signal Q′ is observed to accelerate with regard to the static state period A4, wherein the camera body 1 is intended to remain stationary, until such time as the angular velocity signal Q′ is normalized as a consequence of the discharge of the charge in accordance with the time constant τ of the high-pass filter.
Accordingly, when performing a photography immediately after transitioning to the static state period A4, as an instance thereof, the angular velocity signal Q′ is not fully normalized, and the angular velocity signal Q′ is thus obtained so as to cause the camera body 1 to appear to be making a large movement, despite the camera body 1 actually being stationary, and thus, performing the correction of the movement of the shaking hand in accordance with the angular velocity signal Q′ that results therefrom will result in a significantly blurred photograph.
Thus, a movement of the shaking hand/pan-tilt determination unit is incorporated into a conventional imaging device. When it is determined by the movement of the shaking hand/pan-tilt determination unit that a pan or a tilt is taking place, it is thereby possible to take a photograph without waiting for the charge that is accumulated in the high-pass filter to be caused thereby to rapidly discharge, and for the angular velocity signal Q′ that is thus outputted from the high-pass filter to be normalized by way of the time constant.
The movement of the shaking hand/pan-tilt determination unit determines that either a pan photograph or a tilt photograph is being performed when the angular velocity signal sustains a value that is greater than a prescribed threshold value over a prescribed time.
The movement of the shaking hand/pan-tilt determination unit determines, however, that the pan photograph, or the tilt photograph, is taking place based only upon the size of the angular velocity signal, regardless of whether or not the actual angular velocity of the camera body 1 is accelerating or decelerating. Thus, it is not possible to correctly detect a timing whereat an actual acceleration of the camera body 1 ends and a transition to a driving at a uniform speed takes place, as well as a timing whereat a deceleration of the camera body 1 ends and a transition to the stationary state takes place, and a fault occurs with the correction of the movement of the shaking hand, such as when the camera body 1 is taking a photograph while driving at the uniform speed, i.e., a tracking shot, or when the camera body 1 is taking a photograph immediately after coming to a stop.